In many electrified vehicles, including hybrid electric vehicles, energy that places the vehicle in motion is partially recovered during vehicle braking using what is known as regenerative braking. Regenerative braking can be achieved during braking by configuring the drive motor as a generator. The act of generating power with the motor creates a braking torque, or regenerative torque, on the motor. Regenerative torque is transmitted to the wheels to slow the vehicle. In many situations, regenerative torque alone cannot meet a braking request and, therefore, the regenerative torque is combined with friction braking (e.g., disc or drum braking).
In some known systems, such as that which is graphically illustrated in FIG. 1A, the driveline between the wheels and the motor is fully locked. In this system, when a user initiates a braking request (e.g., presses the brake pedal), the driveline will transmit regenerative torque from the motor to the wheels. In another known system, such as the system graphically illustrated in FIG. 1B, a torque converter between the motor and the wheels must be fully locked (e.g., by actuating a torque converter bypass clutch, for example), before any regenerative torque is applied. After the torque converter is fully locked, the regenerative torque is introduced abruptly, at a level equivalent to a regenerative torque limit.